(i) Field of the Invention
The present invention relates to a method for evaluating the surface state of a polished silicon wafer, and more specifically it relates to a method for evaluating the terminal bond state of different kinds of atoms on the surface of a silicon wafer, a natural oxide film, or molecular pollutants adhered onto the wafer surface in accordance with a multi-internal reflection method.
(ii) Description of the Prior Art
Heretofore, for the elemental analysis of the surface of a substance, there can be utilized, for example, an X-ray microanalyzer which comprises irradiating a sample with electron beams, and an ion micro-analyzer which comprises irradiating the sample with ion beams. According to these techniques, the kinds of elements on the surface and the structure of the surface can not be analyzed without destroying the surface.
Furthermore, another multi-internal reflection method has been suggested by Takahagi et al. in which silicon crystal itself is used as an internal reflection element and an incident angle is larger than a critical angle [T. Takahagi, I. Nagai, A. Ishitani, H. Kuroda, and Y. Nagasawa, J. Appln. Phys., 64, 3516 (1988)], and they have reported on the bond state of the different kinds of atoms on the silicon surface being an Si-H bond and the oxidation process of the surface.
However, in most cases of these analytical methods of applying the certain kind of beams, the sample must be disposed in vacuo, and a chemical bond on the surface may be destroyed on occasion, depending upon the energy of the beams. Thus, some restriction has been put on these techniques.
Additionally, in the multi-internal reflection method suggested by Takahagi et al. in which silicon itself is used as the internal reflection element, this internal reflection element as a reference must have a chemically clean silicon surface and this surface state must be well known. Accordingly, it has been substantially impossible to directly evaluate the surface of the silicon wafer.
FIG. 7 is a spectrum drawing obtained by measuring an oxide film on the silicon surface in accordance with an infrared multi-internal reflection method in which the silicon crystal is used as the internal reflection element. The transmittable wave length range of silicon extend from 1.1 to 6 .mu.m (9,100 to 1,700 cm.sup.-1), and therefore the measurement is possible in the wave length range of about 2,000 cm.sup.-1 or more, but chemical species having absorption bands at wave-numbers (1/wave length less than the wave numbers can not be observed.
However, it is necessary to directly evaluate the surface of the silicon wafer from the viewpoint of controlling a wafer manufacturing process. For example, a washing treatment step with a hydrofluoric acid solution is a pretreatment step for a silicon device process such as a thermal oxidation step or an epitaxial growth step, and it is strongly desired from the viewpoint of the process control to evaluate the wafer surface treated in this step.